We are developing a novel immunomodulatory therapy, hR-411, to treat relapsing-remitting multiple sclerosis (RRMS). hR-411 restores regulatory T-cell balance by redirecting pathogenic Th1/Th17 cells into tolerance- inducing Tr1 cells. hR-411 is formed from the fusion of human Ig-Fc and CXCL11, a CXCR3-binding ligand that has been recently identified as a counter-regulatory chemokine. In contrast to the pro-inflammatory CXCR3- binding ligands CXCL9 and CXCL10, in vitro exposure of inflammatory effector Th1 and Th17 cells to CXCL11 redirects their polarization into anti-inflammatory Tr1 (FOXp3-CD25-IL-10high) cells. mR-411, the murine homologue of hR-411, profoundly suppresses the neurological and histologic findings of murine EAE, even when initiated after disease onset. The durability of this repolarization is shown in adoptive transfer studies wherein Ag-specific effector Th1 cells isolated from murine EAE donors treated in vivo with mR-411 suppress EAE in recipients with active disease. In contrast to general immunosupresants (steroids, rapamycin, calcineurin inhibitors), mR-411 induces tolerance that is Ag-specific for active disease yet preserves historical cell-mediated immunity to unrelated Ag's. Because CXCL11 interacts via the CXCR3 receptor, it is expected to bypass the CD46 defect in CD4+ cells in MS and fully activate IL-10 expression and induce Tr1 cell polarization. In support of this assumption, CXCL11 strongly induces IL-10 expression in human CD4+ cells co-incubated in vitro with anti-CD28. The purpose of this grant is to establish the pharmacodyamic profile of mR-411 in a classic murine EAE model of relapsing MS (R-EAE). The scientific hypothesis to be tested is that mR-411 decreases R-EAE by inhibiting the activation and differentiation of autoantigen-specific pro-inflammatory Th1/Th17 responses predominantly by promoting the activation of Tr1 cell function. Aim #1: Establish a pharmacodynamic profile of mR-411 in a murine model of R-EAE A titration of mR-411 (1, 3, or 10 mg/kg QOD IP) or an irrelevant IgG1 control will be tested in R-EAE, with groups of mice receiving treatment after the acute phase of disease (16-21 days). These treatment groups will be compared to a negative (sham) control group not exposed to PLP139-151, and a positive control group treated with dexamethasone. Animals will be monitored for overt neurological deterioration over a period of 1 month. Spinal cord tissue will be examined for histologic evidence of inflammation and tissue injury. Aim #2: Determination of the in vivo mechanism by which mR-411 decreases disease severity in R-EAE We will test the working hypothesis that mR-411 treatment decreases EAE disease severity by inhibiting the activation of autoantigen-specific Th1/Th17 effector responses. The same experimental paradigm will be employed as in Aim #1. We wil determine how mR-411 treatment alters the number, phenotype, induction, and function of CD4+ Th1/Th17 cells present within the CNS, spleen, and draining lymph nodes following treatment. These studies will use a combination of actively induced and transfer models of EAE employing myelin-specific 5B6 PLP139-151-specific TCR transgenic T cells.